Horizontal-axis wind turbines for generating electricity from rotational motion are generally comprised of one or more rotor blades each having an aerodynamic body extending outwards from a horizontal shaft that is supported by, and rotates within, a wind turbine nacelle. The nacelle is supported on a tower which extends from the ground or other surface. Wind incident on the rotor blades applies pressure causing the rotor blades to move by rotating the shaft from which they extend about the horizontal rotational axis of the shaft. The shaft is, in turn, associated with an electricity generator which, as is well-known, converts the rotational motion of the shaft into electrical current for transmission, storage and/or immediate use. Horizontal-axis wind turbines are generally very well-known and understood, though improvements in their operation to improve the efficiency of power conversion and their overall operational characteristics are desirable.
Incident wind at even low speeds can cause the rotor blades to rotate quickly. As would be well-understood, for a given rotational velocity, the linear velocity of a rotor blade is lowest in the region of its root—the portion of the rotor blade proximate to the shaft. Similarly, the linear velocity of the rotor blade is highest in the region of its wingtip—the portion of the rotor blade distal from the shaft.
Wind turbines are increasing in popularity in recent years as a means of generating renewable energy. With this growth, there is increasing interest in turbine components that are efficient to maintain in good working condition and in methods of efficiently manufacturing components for the wind turbines and optimal locations for their operation have been subsequently declining, with these locations being limited.
It is known that current wind turbine blades are exposed to cyclical gravitational loading and edgewise loading during rotation, also known in the industry as ‘breathing’, where the blade expands and contracts. The expansions and contractions place stress on the bonding seams of rotor blades at the leading and trailing edge, as well as along spar cap and shear webs of the rotor blades. Through this continued stress, trailing edge, leading edge and transverse longitudinal cracks form, leading to eventually delamination and failures. The failures are thought to be a result of the Brazier effect, where over time the breathing causes steadily increasing curvature in the bonding seam areas leading eventually to a threshold curvature after which the object being curved becomes unstable and forms somewhat of a kink.
Various proposals for addressing the stresses placed on rotor blades have been made.
For example, PCT International Patent Application No. PCT/DK2009/000149 to Jensen, entitled “A REINFORCED WIND TURBINE BLADE” discloses an elongated reinforcing member connected to the shell of a wind turbine blade to improve the resistivity to compression forces experienced by the blade.
United States Patent Application Publication No. 2007/0189903 to Eyb, entitled “WIND TURBINE ROTOR BLADE” discloses a carbon fibre reinforced spar cap.
United States Patent Application Publication No. 2009/0129925 to Vronsky et al. entitled “WIND TURBINE BLADE LOAD SENSOR” discloses a wind turbine rotor blade root load sensor configured to be internally mounted within an insert of a root portion of a wind turbine rotor. The sensor is positioned along the internal wall of the root of a rotor blade, and detects torque and other bending forces.
United States Patent Application Publication No. 2009/0277266 to Wang entitled “METHODS AND APPARATUS FOR SENSING PARAMETERS OF ROTATING BLADES” discloses a method for monitoring operating parameters of a rotating blade having at least one sensor thereon, the sensor operatively coupled to a data acquisition device, where the data relates to blade acceleration measurements.
United States Patent Application Publication No. 2009/0232635 to Menke entitled “INDEPENDENT SENSING SYSTEM FOR WIND TURBINES” discloses a wireless sensing device for use in a wind turbine measuring multiple parameters and having an independent power source.